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Reactive in Practice: An Introduction

Reactive in practice: A complete guide to event-driven systems development in Java is a 12 part series that takes learners through the entire spectrum of a real-world event-sourced project from inception to deployment. This reference architecture is to support the series, originally published on IBM Developer:

Complete examples of this material are very sparse in the industry because they are so time intensive to create. However, with the support of IBM and the IBM Developer portal, we've brought this material to life. We hope it inspires the community and showcases best practices of these technologies. Special thanks to Lightbend for peer review assistance.

The main technologies showcased:

  • Java
  • Lagom
  • Play
  • Kafka
  • Cassandra

Published units of learning materials

This reference architecture is meant to enhance the learning experience of Reactive in Practice, a 12 part learning series published by IBM. Please visit the learning materials below to learn about CQRS and event sourcing using Lagom and Vue.


If you would like to contribute, fork this repo and issue a PR. All contributions are welcome!


The following will help you get set up in the following contexts:

  • Local development
  • Deployment to local Kubernetes (using Minikube)
  • Interactions (UI, command line)

Local development and running locally

Most of your interaction with Lagom will be via the command line. Please complete the following steps.

  1. Install Java 8 SDK
  2. Install sbt (brew install sbt on Mac)
  3. Sign up for a free IEX Cloud account for a sandbox stock quote service
    • IEX Cloud is used for stock quotes and historical stock data
    • Click "sandbox mode" from the main landing page to avoid production limits (see instructions on IEX Cloud for more info)
    • Update quote.iex.token="YOUR_TOKEN_HERE" with your API test key in broker-impl/src/main/resources/application.conf and (test keys from IEX start with T)
  4. Sign up for a free Rollbar account and create an access token for front-end logging
    • obtain an access token
    • edit ui/.env and ensure VUE_APP_ROLLBAR_ACCESS_TOKEN is set to your token
  5. Running Lagom in development mode is simple. Start by launching the backend services using sbt.
    • sbt runAll

The BFF ("backend for frontend") exposes an API on port 9100.

Setting up an IDE

Lagom should import fine into IntelliJ IDEA and VSCode. A few pieces of advice:

  • Lagom requires Java 8 compatibility mode for compilation. We recommend installing Java 11 as your default JDK and the compilation target to Java 8. This combination will provide the best ergonomics and support.
  • Reactive Stock Trader makes heavy use of Lombok, a persistent collections framework for Java. You should find the appropriate IDE extensions for Lombok to avoid (significant) IDE warnings.

Testing the backend with CURL

Let's ensure Reactive Stock trader is running properly before wiring up the UI. Do do this, we'll use curl and jq from the command line.

The jq command line tool for JSON is very handy for pretty printing JSON responses, on Mac this can be installed with brew install jq.

The following curl commands will create a new portfolio and then place a few orders to ensure that all microservices are functioning correctly.

# open a new portfolio
PID=$(curl -X POST http:/localhost:9100/api/portfolio -F name="piggy bank savings" | jq -r .portfolioId); echo $PID

# check the portfolio (you should see a lack of funds)
curl http://localhost:9100/api/portfolio/$PID | jq .

# transfer funds into the portfolio
curl -X POST http://localhost:9100/api/transfer -F amount=20000 -F sourceType=savings -F sourceId=123 -F destinationType=portfolio -F destinationId=$PID

# check the portfolio (you should see new funds)
curl http://localhost:9100/api/portfolio/$PID | jq .

# purchase shares in IBM
curl -X POST http://localhost:9100/api/portfolio/$PID/order -F symbol=IBM -F shares=10 -F order=buy

# you should see less funds and now hold shares of IBM
curl http://localhost:9100/api/portfolio/$PID | jq .

If all backend services are configured correctly, you should see the following output:

  "portfolioId": "93ce709d-c15d-4277-b973-1e41c5d2be09",
  "name": "piggy bank savings",
  "funds": 18654,
  "holdings": [
      "symbol": "IBM",
      "shareCount": 10,
      "marketValue": 1323

Configuring and launching the UI

The UI is developed in Vue.js. You'll need to have Node.js and npm installed and then follow the instructions below.

Project setup and launching for development:

npm install
npm run serve

This will launch the UI on localhost:8080 for development. You can then use the UI to interact with the Lagom system.

Testing / debugging:

  • Run your tests: npm run test
  • Lints and fixes files: npm run lint

Deploying to Kubernetes

For instructions on how to deploy Reactive Stock Trader to Kubernetes, you can find the deployment instructions and Helm Charts for Kafka and Cassandra here:


A reference architecture for stock trading to demonstrate the concepts of reactive systems development. Based on the original Stock Trader by IBM and implemented with Lagom by Lightbend.





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